Bargaining council nightmare

[Dave A]

First question is it compulsory to join?

If your scope of activity falls within the scope of the bargaining council, and the agreements have been extended to non-parties by the Minister of Labour, then yes.
If the agreements have not been extended to non-parties, the answer gets a bit more complicated.

and if so which one do I join?

They are in the process of registering me with MEIBC

Now that absolutely fascinates me.
You say you're an electrical contractor, but what exactly is the scope of your activities?

Ordinarily electrical contractors fall under the scope of the NBCEI.

And the big thing is the minimum wage requirements.
R28/h minimum for anyone ie (the guy sweeping my floors.)
Thats R4480pm

I compared some of the minimum pay rates between the two (general worker/minimum paid worker and the driver rates in particular), and it looks like the employer is better off with the NBCEI pay rates by quite some margin. Of course that's not the whole story - you also need to compare company contribution levels for council fees, pension funding etc. as well as well as rates for more skilled staff too to get an overall picture, but the gap between the two is pretty big already just looking at the minimum pay rates.